4 Culprits That Cause Dark Spots (Besides the Sun)

1. Gritty scrubs "They can be harsh on your skin," says Joshua Zeichner, director of cosmetic and clinical research in dermatology at Mount Sinai Medical Center in New York City. "If you overuse them, they cause inflammation, and that increases melanin production—which makes existing spots worse and causes new ones."

2. Pimples Just when a pimple has finally disappeared, a brown spot can emerge in its place. (That's because pimples stress your skin, triggering melanin production.) "Treat the pimple with 1 percent hydrocortisone cream until it subsides and for a day or two afterward," says Zeichner. "It calms the inflammation."

3. Hormones An increase in estrogen—e.g., from pregnancy or birth control pills—can cause the muddy-looking splotches known as melasma. But here's the good news: "Hormones make you more susceptible to melasma, but it flares up only after sun exposure," says Patricia Farris, a clinical associate professor of dermatology at Tulane University in New Orleans. And that's one more reason to wear a broad-spectrum SPF 30 or higher every day.

4. Lightbulbs This is nuts, but even light from lightbulbs can trigger splotches on dark skin, according to a recent study in the Journal of Investigative Dermatology. "Visible light causes pigment production the exact same way that UV light does," says David Bank, an assistant clinical professor of dermatology at Columbia University/Presbyterian Hospital. So now you have yet another reason to apply sunscreen faithfully every day—but not just any sunscreen. "Mineral sunscreens with zinc oxide or titanium dioxide are the only ones that protect against the full spectrum of light," Bank says. Heliocare, an antioxidant pill that's sold at drugstores, has also been shown to hinder the effects of both visible and UV light on skin, according to Vivian Bucay, a dermatologist in San Antonio. And no, it can't replace actual sunscreen.